I've owned a lot of touch devices from the Nokia 7710, the Nokia n97, the N8 and the Nokia N900. And do you know what they have all in common other than the Nokia badge? It's scratches. After a couple of months of use the screen is a haze of minor scratches and lines.
In the beginning a few scratches here and there are not such a big deal. But with use they add up and pretty soon you end up with a really dirty screen. I've tried a good share of screen guards and while they promise to be scratch proof they have yet to stand by it.
The other day while I was browser shopping at MobileFun, I came across the Zagg InvisibleShield for my Nokia n900. With my experience I decided at once that I won't waste more of my monies on that accessory. And I continued searching for any new cool gadgets they might have (check out AngryBird cases and the kindle page).